The invention relates to an ink jet printer and an ink jet print head which comprise plural driving elements for ejecting ink, plural individual flow paths respectively corresponding to the nozzles, ejection ports corresponding to the flow paths, and a common liquid chamber for supplying ink to the individual flow paths, and in which ink is supplied to the common liquid chamber through an ink supply path.
Conventionally, as typical examples of an ink jet print head used in an ink jet printer, known are a piezoelectric ink jet print head in which a pressure chamber is mechanically deformed by a piezoelectric material and ink is ejected through an ink ejection port by the resulting pressure, and a thermal ink jet print head in which a heater disposed in the vicinity of an ink flow path is energized to evaporate ink and ink is ejected through an ink ejection port by the pressure produced by the evaporation.
FIG. 17 is a perspective view showing the vicinity of a head chip and an ink supply member in an example of an ink jet print head of the prior art, and FIG. 18 is a section view taken along a line A. In the figures, 1 designates a head chip, 2 designates nozzles, 3 designates individual flow paths, 4 designates heating elements, 5 designates a common liquid chamber, 6 designates a heat sink, 7 designates a circuit board, 8 designates bonding wires, 9 designates a sealant, 10 designates air bubbles, 11 designates an ink supply member, 12 designates an ink supply device, and 13 designates an ink flow pipe. FIGS. 17 and 18 show a thermal ink jet print head.
In the head chip 1, the plural individual flow paths 3 are formed and open in the outside so as to form the nozzles 2. The individual flow paths 3 internally communicate with the common liquid chamber 5. The heating elements 4 are disposed at midpoints of the individual flow paths 3, respectively. When the heating elements 4 generate heat, air bubbles are produced in the individual flow paths 3. The pressure of the produced air bubbles causes ink drops to be ejected through the nozzles 2, thereby performing the recording. The common liquid chamber 5 has an opening functioning as an ink inflow port.
The head chip 1 may be produced by, for example, bonding two silicon substrates together. In this case, the individual flow paths 3, the common liquid chamber 5, etc. are formed in one of the silicon substrates by anisotropic etching. The common liquid chamber 5 is formed by the anisotropic etching so as to pass through the silicon substrate, and the through hole is formed as the opening functioning as the ink inflow port. In the anisotropic etching, the silicon substrate is etched so as to form a predetermined angle. Therefore, each individual flow path 3 is formed into a triangular shape and the common liquid chamber 5 is formed into a shape which is expanded as moving from the opening to the inner portion. The communication between the individual flow paths 3 and the common liquid chamber 5 is directly performed by the anisotropic etching, or formed by grinding an unetched portion by means of dicing. Alternatively, a resin layer formed on the other substrate is etched to form bypass pits, thereby realizing the communication.
The ink supply member 11 has the ink supply device 12 and the ink flow pipe 13 which are used for supplying ink fed from an ink tank (not shown) to the head chip 1. The ink supply device 12 is formed as a substantially chevron space so that the opening is larger than the opening of the common liquid chamber 5 of the head chip 1. The object of this structure is to prevent ink turbulence from occurring, thereby reducing residual air bubbles. This structure is described in, for example, the Unexamined Japanese Patent Application Publication No. Hei 6-91874. The ink supply member 11 is fixed to the head chip 1 in such a manner that the opening of the ink supply device 12 communicates with that of the common liquid chamber 5 of the head chip 1.
The head chip 1 is fixed to the heat sink 6 so as to dissipate heat generated by the heating elements 4. Also the circuit board 7 is disposed on the heat sink 6 so that the power and signals supplied from the main unit of the printer are transmitted to the head chip 1 through the bonding wires 8, and signals and the like of various sensors disposed in the head chip 1 are transmitted to the printer main unit. In order to protect the bonding wires 8 and reinforce the fixation of the head chip 1 and the ink supply member 11, the sealant 9 is poured into a space defined by the ink supply member 11 and the heat sink 6.
Ink is fed from the ink tank which is not shown to the thus configured ink jet print head. The ink fed from the ink tank is supplied to the ink supply device 12 through the ink flow pipe 13 in the ink supply member 11, and then to the common liquid chamber 5 of the head chip 1 so as to be further supplied to the individual flow paths 3. The nozzles 2 open in the air. When no countermeasure is taken, therefore, ink leaks from the nozzles 2. To comply with this, the interior of each ink flow path is always maintained to have a negative pressure of 0 to -200 mmH.sub.2 O by an ink impregnating member in the ink tank or a negative pressure generating mechanism.
In the ink jet print head, when air bubbles 10 stay in the ink supply device 12 or the common liquid chamber 5, the air bubbles 10 grow while the printer is used. The air bubbles 10 close the individual flow paths 3 so as to impede the ink supply, with the result that a printing failure is caused. In the thermal ink jet print head, particularly, ink is evaporated by heat generation of the heating elements 4, and hence the temperature of the ink is raised by the heat generated in this process. Then, air in the ink is precipitated and the air bubbles 10 in the common liquid chamber 5 gradually grow. Even in the case where only small air bubbles initially stay, therefore, the air bubbles finally impede the ejection. Since the growth of air bubbles is based on the heat generation as described above, air bubbles 10 tend to grow in the common liquid chamber 5 and at a portion where the ink supply device 12 is connected to the common liquid chamber 5. In the configuration described above, since the opening of the ink supply device 12 is larger than that of the common liquid chamber 5, the peripheral portion of the opening of the common liquid chamber 5 impedes the ink flow, so that air bubbles 10 easily grow in this portion. The air bubbles 10 which have grown to a larger size then enter the common liquid chamber 5 to impede the supply of ink to the individual flow paths 3, thereby causing an image defect.
FIG. 19 is a diagram illustrating the ink flow in the ink jet print head of the prior art, and FIG. 20 is a graph showing an example of the flow rate of ink in the head. As means for preventing an image defect due to air bubbles staying in the common liquid chamber from occurring, a method in which air bubbles staying in the common liquid chamber are removed away by sucking them through the nozzles 2 is usually employed. In FIG. 19, the arrows show the direction of the ink flow in the suction process. FIG. 20 shows the flow rates in the direction of the ink flow in various portions in this process. Also in a usual printing process, the ink flow direction is substantially identical with that shown in FIG. 19.
When ink is sucked through the nozzles 2, a quantity of ink which is equal to that of the sucked ink is fed from the ink tank which is not shown. The ink is supplied through the ink flow pipe 13 and enters the ink supply device 12. The ink then spreads along the shape of the ink supply device as shown in FIG. 19, and the flow rate is reduced as shown in FIG. 20. The ink in the ink supply device 12 further flows in the direction from the ink supply device 12 to the common liquid chamber 5 and then enters the common liquid chamber 5. The inferior of the common liquid chamber 5 is somewhat expanded, and hence the ink flow rate is further reduced. The direction of the ink flow which enters the common liquid chamber 5 is changed toward the individual flow paths 3, and then sucked out through the individual flow paths 3. Since the individual flow paths 3 have a small sectional area, the ink flow rate is higher.
When ink flows as described above, the ink flows are uniform in all the nozzles and hence a higher image quality can be realized. When air bubbles 10 stay in the common liquid chamber 5, however, the low ink flow rate in the common liquid chamber 5 makes the removal of the air bubbles 10 difficult. Furthermore, also the rate of the ink flow in the ink supply device 12 is low. Accordingly, when air bubbles 10 stay at a step formed in the portion where the ink supply device 12 is connected to the common liquid chamber 5, for example, the air bubbles 10 are hardly sucked even by conducting such a suction process. Consequently, the suction process fails to suck all the air bubbles 10 and the air bubbles tend to stay in the portion, with the result that an image defect which is so serious that a further suction process must be immediately conducted is produced. As a countermeasure, it may be contemplated that the suction process is repeated several times. As the suction process is conducted more frequently, however, the ink utilization efficiency for printing is lower, and a waste ink tank which is required for storing sucked ink must have a larger capacity, thereby producing a problem in that the size of the whole of an apparatus is increased.
Another configuration in which the side wall of a common liquid chamber is formed at an angle of 45.degree. or less which is smaller than that in the above-mentioned configuration is described in, for example, the Unexamined Japanese Patent Application Publication No. Hei 3-110172. Also in this configuration, the ink flow spreads into a fan-like shape, and hence there arises the same problem as that discussed above.